Backing paper for roll photographic film



Nov. 8, 1960 E. L. BAXTER ETAL 2,959,492

BACKING PAPER FOR ROLL PHOTOGRAPHIC FILM Filed Feb. 13, 1959 PRINTING l5 TRANSHIRDVT ZEIN l3 ZEIN CONTPIIWNG CHROME YELLOW CHROME ORANGE AND THIN/UM DIOXIDE 10 PA PER ll CARBON BLACK IN STYRE NE -BUTADIENE COPOLYMER L2 CARBON BLACK IN ETHYLCELLUIDSE Fig].

*24 PRINTING 25 TRANSPARENT ZEIN 23 STYRENEBUTADIENE COPOLYMER Fi .2 ammzaraziszz 20 PAPER 1 ////////////////////79 BLACK gym E fggifgffifiiflfimflw'l 34 PRINTING "35 TRANSHIRENT Z EIN 33 VINYLIDENE CHLORIDE-ACRYLONITRILE copounzn CUNTHlN/NG MEDIUM CHROME YELLOWAND 'nmNIuM moxms 3O PAPER 3' CARBON BLACK IN STYRENE-BUMDIENE COPOLYMER 32 cnnaou BLACK 11v ernncawwsz L\\'k"fi 'IIIIIIIIIIIIIIIIIIIIII Fig. 3

.Ernesi L. Baxter Martin S alo Maw ATTORNEYS United States Patent Rochester, N.Y., as-

Ernest L. Baxter and Martin Salo,

Rochester, N.Y.,

signors to Eastman Kodak Company, a corporation of New Jersey Filed Feb. 13, 1959, Ser. No. 793,177

4 Claims. (Cl. 117-14) This invention relates to backing paper for roll photographic film, and more particularly relates to an improvement in the backing paper, described in Patent 2,751,309 of June 19, 1956, which has protective light-colored and opaquing coatings thereon and is characterized by having an overall thickness appreciably less than conventional backing papers, and is superior in opaqueness to duplex backing paper.

As is well understood, a photographic roll film cartridge generally comprises a flanged spool upon which is wound a long strip of backing paper to which, before winding, has been attached on one side thereof a strip of light sensitive photographic film. The ends of the backing paper are positioned to extend beyond the ends of the film and constitute light protective leader and trailer strips for film which is interwound with the backing paper so that it separates adjacent convolutions of the film.

T o assure opaqueness, backing paper conventionally employed for roll film consists of a duplex paper with one side being black and the other side being colored with v a characteristic identifying color. The duplex paper may be made by means of a Fourdriner paper machine and a cylinder paper machine. The two sheets are brought togethers wet under the first press and thus form a composite sheet of duplex backing paper.

In a commonly available roll film cartridge, the film is attached to the black side of the duplex backing paper, the side of the backing paper opposite that contacting the film being differently colored and carrying various printed symbols such as the number of exposed areas, warning marks, and advertising matter over which is coated a protective layer intended to protect the sensitive emulsion from the paper and ink employed in printing when the film and paper are interwound in close contact. It has been the practice to depend entirely on the duplex paper to prevent transmission of light which would act on the film in the roll in loading and unloading the camera or through the camera window.

In the aforementioned Patent 2,751,309, there is described a new type of backing paper which, instead of a duplex paper, comprises a thinner, single sheet paper having unique chemical coatings thereon. This single sheet paper has a strength at least equal to the thinnest duplex papers now produced and anopacity equal to such duplex papers. The opacity is dependent primarily on the novel chemical coatings on the paper rather than the paper structure itself. This coated backing paper is also very flexible and the coatings withstand the winding incident to placing the backing paper and attached film on the spool.

As will be apparent from Patent 2,751,309, the black side of the backing paper comprises a layer either of carbon black in a vinylidene chloride-acrylonitrile copolymer or of carbon black in a styrene-butadiene copolymer.

Backing paper with a black layer made of carbon black in a styrene-butadiene copolymer is preferred, however, an unforeseen disadvantage was experienced with its use. Blocking of the styrene-butadiene to the zein coating on the opposite side occurs in the coating operation. Blocking also occurs between the styrene-butadiene coating and 2,959,492 Patented Nov. 8,1960

the back surface of the roll film when spooled. 'In separating the backing paper and film in the processing operation, static discharges are produced on the film from this blocking action. Under conditions of high relative humidities and temperatures Such as are encountered, for example, in the tropics, the back surface of the roll film becomes tacky with the result that it sticks to the surface of the backing paper with which it comes in contact. Under such extreme climatic conditions the sticking is occasionally so bad that chunks or areas of the black side are pulled off the paper. The photofinisher encountering roll film adhered to Duplex paper can, by prolonged washing and manipulation, wash off the black paper fibers and salvage some of the prints for the customer. When zein-carbon black, styrene-butadiene carbon black areas become cemented to the back surface of the film, it is extremely difficult for the photofinisher to remove these cemented portions and the customers negatives, in most cases, are a complete loss.

We have found that the tacky back surface of the film under high humidity adheres very tightly to carbon blackzein layers as well as to numerous other types of materials.

An object, therefore, of the present invention is to provide an improved backing paper structure in which the advantages of the single sheet backing paper of Patent 2,751,309 are retained and the above-described static and I sticking tendencies are eliminated.

. which is then overcoated with carbon black in an ethyl cellulose binder. This carbon-ethyl cellulose layer will eliminate blocking of the backing paper and hence static ditficulties occasioned thereby. The opposite side .of the paper is coated with a plurality of lighter colored coatings. Printing may be placed on the lighter colored side of the backing paper and, if so printed, the printed side maybe given a transparent protective overcoating to protect the film emulsion from the printing inks. The various coatings may be applied in proper sequence by a rotogravurc process or by other suitable coating processes such as described hereinafter. The coatings may be suitably dried between applications.

The paper preferably employed as the base of the backing paper structure is a 14 pound per 1000 sq. ft. paper made of a purified fiber or of unpurified fiber such as unbleached natural color kraft paper which is conditioned to 4-12% moisture content and su'percalendered to a thickness of 0.0025 to 0.0030 inch. The compositions of each of the black coatings and each of the light-colored coatings are further described hereinafter.

BLACK COATINGS The following two examples describe the composition of suitable black opaquing coatings which are applied directly to one side of the paper:

Example I Percent I Styrene-butadiene copolymer (50-70% styrene) (48% solids in aqueous colloidal dispersion) Carbon black Sodiun salt of partially desulfonated lignin sulfonic aci NaOH Water (48% solids in aqueous colloidal dispersion) 19.8

Carbon black 16.0 Water 63.3 Sodium salt of partially desulfonated lignin sulfonic acid 0.80 NaOH 0.08

In preparing the black colored dispersions, the selected resin copolymers are added with stirring to a 30-40% aqueous carbon dispersion. The carbon dispersion is made by adding the carbon to water containing as a dispersing agent the sodium salt of the partially desulfonated lignin sulfonic acid and caustic soda is added to control the pH within the range of :1.

The black coating of Example II is preferred.

BLACK OVERCOATING Example III Percent Ethyl cellulose 5.0 Carbon black 5.0

Ethyl alcohol 90.0

This formulation is mixed by thorough stirring. A suitable ethyl cellulose is Dow Ethocel Type 10. It has a relatively low viscosity and a high solubility in ethanol. The resulting ethyl cellulose-carbon coating gives complete freedom from static and sticking.

YELLOW COATINGS The following three compositions may be employed for coating the light-colored side of the backing paper.

Example IV Pounds Zein 20 Medium chrome yellow 10 Light orange (chrome) 5 Titanium dioxide Isopropyl alcohol 64 Water 16 Staybelite (hydrogenated rosin)* 1.2

A pale, medium hard, thermoplastic resin made from hydrogenated wood rosin; acid number 162; softening point 76 C. density 1.045 at 20 C.

Example V Percent Styrene-butadiene copolymer (50 to 70% styrene) In these formulas the titanium dioxide pigment is finely divided; medium chrome yellow is a finely divided metal chromate pigment; light orange is a finely divided metal chromate pigment. Zein is employed as the binder in the yellow coating of Example IV and the protective overcoating, since it will not fog or desensitize the photographic emulsion of the film.

A suitable rotogravure process for applying these coatings to the paper base of the backing paper is described in U.S. Patent 2,218,249 of October 15, 1940. The various applications are made continuously and each coating is dried before the next is applied. The coating is applied to the paper by the intaglio roll which is rotatably mounted in a pan containing the coating solution. The surface of the intaglio roll is embossed, providing a plurality of very minute cups which carry the solution, the excess solution being removed from the intaglio roll by a doctor blade. The solution in these various cups is then transferred or applied uniformly to the strip by pressing the strip firmly against the cups by means of a rubber pressure roll over which the strip is fed. Each of these deposits, after being placed on the paper, is merged into a continuous layer by means of a smoothing bar to provide a uniform coating over the entire paper surface. Each coating is preferably dried in heated air having a relative humidity of 6% at F. before applying a second coating.

The various coatings described herein may also be applied to our backing paper base by the roll and air knife method generally described in Patent 1,980,923 of November 13, 1934. The selected black coating is applied first to one side of the single sheet backing paper and spread by the air knife. This black coating is dried at -200" F. by being passed through a heated drying chamber. In some instances a plurality of black coatings may be spread onto the black side of the backing paper by alternate coating and drying steps.

Suitable ink compositions for printing indicia by rotogravure processes on the backing paper are disclosed in Patent Re. 21,268 of November 21, 1939. These inks comprise suitable coloring materials in a prolamine binder such as zein. Other suitable printing inks for such backing papers are disclosed in Patent 2,262,987 of November 18, 1941.

The invention will be further understood by reference to the drawings in which Figs. 1 to 3 represent a greatly enlarged cross-section of backing paper made in accordance with various forms of the present invention and Fig. 4 shows the novel backing paper of Fig. 1 and photographic film wound on the roll with the film and backing paper separated at one end for purpose of illustrating their relative positions in the roll.

Referring to Fig. l, a cross-section of a strip of bleached kraft paper is shown at 10 having on the lower surface thereof a coating 11 of a layer of carbon black in styrene-butadiene copolymer coated from the composition of Example 1. Layer 11 is overcoated with a layer 12 of carbon black in ethyl cellulose which is coated thereon from the composition of Example III. On upper surface of the paper 10, there is the yellow coating 13 comprising chrome orange and yellow pigments as well as titanium dioxide pigments in a zein binder. This was coated from the composition described in Example IV, supra. The printed indicia is shown at 14 overcoated with a transparent protective zein coating 15. Such a transparent zein protective coating is described in Patent 2,262,987 of November 18, 1941 and is also employed in layers 25 and 35 of Figs. 2 and 3.

Referring to Fig. 2, a cross-section of a strip of bleached kraft paper is shown at 20 having on its lower surface a coating 21 of a layer of carbon black in the styrene-butadiene copolymer coated from the composition of Example II. Layer 21 is overcoated with a layer 22 of carbon black in ethyl cellulose which is coated thereon from the composition of Example III. On the opposite surface of the paper 20 there is a yellow coating 23 comprising chrome yellow and titanium dioxide in a styrene-butadiene binder. This was coated from the composition described in Example V. The printed indicia is shown at 24 overcoated with a transparent zein coating 25.

Referring to Fig. 3, a cross-section of a strip of bleached kraft paper is shown at 30 having on its lower surface a coating 31 of a layer of carbon black in the styrene-butadiene copolymer coated from the composition of Example II. Layer 31 is overcoated with a layer 32 of carbon black in ethyl cellulose which is coated thereon from the composition of Example HI. n the upper surface of the paper 30 there is a yellow coating 33 comprising medium chrome yellow and titanium dioxide in a vinylidene chloride-acrylonitrile copolymer. This was coated from the composition described in Example VI. The printed indicia is shown at 34 overcoated with a transparent zein coating 35.

The backing paper structure described in connection with Fig. 1 is the preferred form of the present invention. However, the backing paper structure shown in any of the Figs. 1 to 3 gives a product that fulfills all the advantages herein, at an economical cost and results in a non-blocking, non-dust producing backing paper when stored under conditions of high humidities and temperatures or when wound through a camera.

Referring to Fig. 4, a film cartridge 40 is shown partly open in which the backing paper of the present invention is employed. This drawing shows the relation of the backing paper surfaces 15 and 12 of Fig. 1 in respect to film 43 when assembled on the spool 40. The emulsion side of the film is shown at 41 and the base side at 42.

While the preferred coating compositions are described above, satisfactory backing. papers may be made by employing the various coating materials in the following ranges:

Preferred range of total composition Compositions: percent Vinylidene chloride-acrylonitrile copolymer of styrene-butadiene copolymer to 25 Black pigment 1 to 20 White pigment 15 to 45 Yellow pigment -1. 15 to 45 Water 50 to 70 Other useful pigments are, for example, Hausa Yellow, Fast Pigment Yellow and any carbon black of suitable dispersion.

Other pigments which are inert to photographic emulsions may be employed. In fact, any choice of pigments of suitable size for this invention is limited only by the requirement that they be without detrimental effect on the photographic film.

THICKNESS OF COATING Black coating composition is applied in two coatings to give a total of 12 lbs. of solution per 1000 sq. foot for satisfactory opacity.

Light pigment composition is applied in the amount of 5 lbs. per 1000 sq. foot to give satisfactory uniformity of color.

-The ethyl cellulose-carbon black coating is applied in .18 lb. per 1000 sq. foot.

Any other type of paper may be employed if it has good strength at least comparable to the present duplex paper. A rag paper, for example, is suitable but, of course, more expensive than kraft paper.

Preferably the average tear strength of a suitable paper should be at least 50 gms. as determined by the Elmendorf tear test. This tear test is described in Paper Trade Journal for June 18, 1942 as Tappi Standard T414M40.

While, as indicated above, kraft paper is particularly suited for employment in my invention, certain other types of paper could be employed instead, such as unbleached sulfatepaper colored with a suitable dye such as Stilbene yellow in which a small amount of filler such as TiO is added to give body and density or opacity to the paper.

These papers comprising the base of the backing paper are of a weight that can be supercalendered to a thinness that the paper itself plus the coatings thereon does not exceed an average maximum thickness of 0.0040 inch. a 15-pound per M sq. ft. paper has been found satisfactory.

The opacity of roll film backing paper is tested in the following manner.

A sheet of the backing paper under test is placed over a sheet of highly sensitive film, such as Super XX Panchromatic film with the black side of the backing paper in contact with the back of the film, duplicating its position on roll film. An orange-red filter of the type employed in camera back windows is placed over the opposite side of the backing paper and the assembly is placed in a printing frame. The test material is exposed to a light intensity of 5000 foot candles for ten minutes. The film is then processed in the usual way and examined for the presence of specks of developed silver. A satisfactory backing paper should show no visible silver image.

The improvement in employing the resinous coatings of the present invention as respects flexibility is shown in the following table:-

(The higher the number the stiffer the paper.)

I Tappi Tentative Method 1451. 1 Tappi Instrumentation Studies XIV.

We have found that our improved backing paper has many advantageous features not possessed by duplex, papers which it may replace. The strength and other physical properties of the paper employed as the base of the backing paper is at least equal to the strength of the thinner duplex papers now available to the trade. The overall thickness can be made as low as 0.0032, up to 0.0045 inch thus permitting extra exposures to be added to present rolls of film without increasing the diameter beyond that of films now in use. The opaqueness, even though the overall thickness is less than backing papers now available in the trade, is better than such backing papers. The backing paper made in accordance with our invention requires the least amount of coating materials, both black and colored, of any of the methods described or known in the trade. The uniformly lightcolored side gives maximum contrast with the legends printed thereon. Also less clock springing of freshly rolled film is experienced with this paper than with the thicker duplex paper. ethyl cellulose-carbon black on the black side of the backing paper solves the difficulty of blocking between adjacent convolutions of the roll and eliminates static discharges. These advantages plus the advantage of applying the coatings by rotogravure and air knife methods, which are fast, accurate and efficient, emphasize the importance of my present invention in this art.

The additional coating of the We claim:

1. In photographic backing paper having an overall thickness less than 0.0045 inch consisting of a single sheet of thin kraft paper which is of a thinness which will permit passage of substantial amounts of actinic light, having on one side a light colored pigmented coating consisting essentially of a yellow pigment in a binder selected from the class consisting of vinylidenechlorideacrylonitrile copolymer, styrene-butadiene copolymer and zein, printed indicia on said lighter colored coating, a clear zein protective coating thereover, and on the opposite side an opaque coating consisting of carbon black in a binder of styrene-butadiene copolymer, the improvement which consists in a protective coating over said opaque coating of carbon black in ethyl cellulose.

2. In photographic backing paper having an overall thickness less than 0.0045 inch consisting of a single sheet of thin kraft paper which is of a thinness which will permit passage of substantial amounts of actinic light, having on one side a light colored pigmented coating consisting essentially of a yellow pigment in a binder of vinylidene chloride-acrylonitrile copolymer, printed indicia on said lighter colored coating, a clear zein pro-- tective coating thereover, and on the opposite side an opaque coating consisting of carbon black in a binder of styrene-butadiene copolymer, the improvement which consists in a protective coating over said opaque coating of carbon black in ethyl cellulose.

3. In photographic backing paper having an overall thickness less than 0.0045 inch consisting of a single sheet of thin kraft paper which is of a thinness which will permit passage of substantial amounts of actinic light, having on one side a light colored pigmented coating consisting essentially of a yellow pigment in a binder of styrene-butadiene copolymer, printed indicia on said lighter colored coating, a clear zein protective coating thereover, and on the opposite side an opaque coating consisting of carbon black in a binder of styrene-butadiene copolymer, the improvement which consists in a protective coating over said opaque coating of carbon black in ethyl cellulose.

4. In photographic backing paper having an overall thickness less than 0.0045 inch consisting of a single sheet of thin kraft paper which is of a thinness which will permit passage of substantial amounts of actinic light, having on one side a light colored pigmented coating consisting essentially of a yellow pigment in a binder of zein, printed indicia on said lighter colored coating, a clear zein protective coating thereover, and on the opposite side an opaque coating consisting of carbon black in a binder of styrene-butadiene copolymer, the improvement which consists in a protective coating over said opaque coating of carbon black in ethyl cellulose.

References Cited in the file of this patent UNITED STATES PATENTS 1,300,056 Tyrrell Apr. 8, 1919 1,915,391 Stoops June 27, 1933 2,227,843 Quenelle Jan. 7, 1941 2,331,715 Nadeau et al. Oct. 12, 1943 2,340,971 Manley et al. Feb. 8, 1944 2,751,309 Baxter June 19, 1956 

1. IN PHOTOGRAPHIC BACKING PAPER HAVING AN OVERALL THICKNESS LESS THAN 0.0045 INCH CONSISTING OF A SINGLE SHEET OF THIN DRAFT PAPER WHICH IS OF A THINNESS WHICH WILL PERMIT PASSAGE OF SUBSTANTIAL AMOUNTS OF ACTINIC LIGHT, HAVING ON ONE SIDE A LIGHT COLORED PIGMENTED COATING CONSISTING ESSENTIALLY OF A YELLOW PIGMENT IN A BINDER SELECTED FROM THE CLASS CONSISTING OF VINYLIDENE CHLORIDEACRYLONITRILE COPOLYMER, STYRENE-BUTADIENE COPOLYMER AND ZEIN, PRINTED INDICIA ON SAID LIGHTER COLORED COATING, A CLEAR ZEIN PROTECTIVE COATING THEREOVER, AND ON THE OPPOSITE SIDE AN OPAQUE COATING CONSISTING OF CARBON BLACK IN A BINDER OF STYRENE-BUTADIENE COPOLYMER, THE IMPROVEMENT WHICH CONSISTS IN A PROTECTIVE COATING OVER SAID OPAQUE COATING OF CARBON BLACK IN ETHYL CELLULOSE. 